
FOR THE 

PROMOTION OF THE MECHANIC ARTS. 

Report of a Special Committee 

Competitive Tests of Dynamo- 
Electric Machines, 

AND ON 

Mechanical and Electrical Tests of 
Conducting Wires. 












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Jour. Frank. Inst., Vol. CXX. Nov., 1883. 

(Tests of Dynamo-Electric Machines.) 



THE TATHAM DYNAMOMETER. 




































































































































































































































































































































































































































FRANKLIN INSTITUTE OF THE STATE OF PENNSYLVANIA 

» r 

FOR THE 

Promotion of the Mechanic Arts. 


Competitive Tests 


OF 


namo 


n 


□ 


u 



nc iviacmnes 


Report of a Special Committee, appointed Ny 
the President of the Franklin Institnte in 
conformity with a Resolution of the 
Hoard of Managers, passed 
November 12, IB El4, 


[ISSUED by AUTHORITY of the BOARD of MANAGERS and PUBLISHED as a 
SUPPLEMENT TO THE JOURNAL OF THE FRANKLIN 
INSTITUTE, NOVEMBER, 1885.] 


PHILADELPHIA : 

THE FRANKLIN INSTITUTE. 

1885. 



















EDITING COMMITTEE. 


PERSIFOR FRAZER, Chairman , 

CHARLES BULLOCK, 

THEO. D. RAND, 

COLEMAN SELLERS, 

WILLIAM H. WAHL. 


i 


2- I3i A 



FRANKLIN INSTITUTE OF THE STATE OF PENNSYLVANIA. 
FOR THE PROMOTION OF THE MECHANIC ARTS. 


To the Board of Managers of the Franklin Institute: 

Gentlemen :—I herewith transmit the report of the Committee 
of Judges, consisting of Louis Duncan, Ph.D., Ensign, U. S. Navy, 
Chairman; William D. Marks, Whitney Professor of Dynamic 
Engineering, University of Pennsylvania; George L. Anderson, 
Lieut. U. S. Army, Instructor of Mathematics, U. S. Military 
Academy, West Point; J. B. Murdock, Lieut. U. S. Navy; A. B. 
Wyckoff, Lieut. U. S. Navy, Hydrographic Office, Philadelphia, 
appointed under authority of the resolution of the Board, adopted 
November 12, 1884, to Conduct Competitive Tests of Dynamo- 
Electric Machines, entered for competition by the Edison Electric 
Light Company, and the United States Electric Light Company, 
who duly accepted them as judges. 

It was found impossible to constitute the committee from the 
list of names in the adopted code, most of those gentlemen declin¬ 
ing to serve, or accepting under unavailable conditions. 

Commander Jewell, U. S. Navy, acted as Chairman at the 
beginning, and rendered valuable assistance and advice in the pre¬ 
liminary preparations. Owing to unavoidable delays, however, the 
tests were not begun before his paramount duties at the U. S. 
Torpedo Station compelled him to withdraw. 

The conditions of the code were severe upon the judges, 
requiring protracted runs of the machines, and immediate calcula¬ 
tions of results. The labors of the committee were therefore 
incessant, and were performed with such zeal, intelligence, fidelity, 
and success as to satisfy me that no praise of mine could exceed 
that to which a careful examination of the report of their work will 
entitle them. 

The thanks of the Institute are due not only to the judges, 
but also to the heads of the Departments and Bureaus of the 
Navy and Army, whose consent was necessary to enable the 
officers to take part in the work. 



4 


The Institute is under especial obligations to the Johns 
Hopkins University for the use of their laboratory and for assistance 
in comparing thermometers and resistances. 

The thanks of the Institute are also due to various parties for 
loans of apparatus, as follows : 

Baldwin Locomotive Works, for use of boiler ; Buckeye Engine 
Company, Salem, O., for steam engine; Professors Genth and Sadtler 
and the department of Dynamics of the University of Pennsylvania, 
for platinum crucibles, indicators, resistance coils and galvanometer ; 
U. S. Coast and Geodetic Survey, for magnetometer; Stevens 
Institute of Technology for tangent galvanometer ; Mr. Wm. Har- 
pur, for chronometer; Mr. Henry Troemner, for delicate balances; 
Messrs. Fairbanks & Co., for beam, platform scales and standard 
weights ; Electrical Supply Company, of New York, for volta¬ 
meter; Commander Jewell, U. S. Navy, and the members of the 
committee, lor the use of their instruments. 

Very respectfully, 

W. P. Tatham, President. 

Philadelphia, September 26, 1885. 


RESOLUTION. 

[Resolutions of the Board of Managers, Nov. 22, 1884.] 
Whereas, Through delay and lack of time on the part of many of the 
Examiners, several of the largest exhibits at the Electrical Exhibition have 
had either incomplete examination or have had none at all; therefore, be it 

Resolved , That the President be directed to take such steps, appoint such 
committees, and incur such expense, not exceeding three thousand dollars, as 
shall be necessary to complete in a satisfactory manner the examination of 
exhibits. 


Mr. W. P. Tatham, President of the Franklin Institute. 

Sir :—I have the honor to herewith transmit the report of the 
Ccmmittee appointed to conduct the Competitive Tests of the 
Dynamo Electric Machines of the U. S. Electric Light and Edison 
Companies. 

I am, very respectfully yours, 

LOUIS DUNCAN, Chairman. 




5 

COMPETITIVE TESTS of DYNAMO-MACHINES. 

On first organizing the committee, Commander Jewell, U. S. N. 
was elected Chairman, but after directing some of the preliminaries, 
he was compelled to resign in order to resume his duties at the 
U. S. Torpedo Station, at Newport. 

The tests were conducted under the following code, agreed to 
by the contestants : 

Proposed Code for Test of Dynamo Electric Machines , to be used by the 
Franklin Institute of the State of Pennsylvania. 


SECTION I. 

GENERAL CLAUSES AND CONDITIONS. 

(i.) The parties hereto subscribing do agree to accept the services of the 
examiners herein named, and to abide by the verdict of the Judges and the 
methods of testing named without appeal from the decision reached. 

LIST OF JUDGES. 

{From which five shall be chosen to act.) 

(2.) Prof. WM. A. ANTHONY, Cornell University, Ithaca, N. Y. 

Prof. WM. D. MARKS, University of Pennsylvania, Philadelphia, Pa. 
Prof. J. E. DENTON, Stevens Institute, Hoboken, N. J. 

Prof. W. E. GEYER, Stevens Institute, Hoboken, N. J. 

Lieut. J. B. MURDOCK, U. S. N., Philadelphia, Pa. 

Ensign LOUIS DUNCAN, U. S. N., Johns Hopkins University. 

Lieut. JOHN MILLISS, Light-House Board, New York. 

OSCAR BUSSMANN, Assistant. 

(3.) The Franklin Institute will procure instruments, pay expenses of 
observers. The companies will pay for handling machines, running lines, 
placing and erecting lamps, and care for machines during test. 

SECTION II. 

CONSTRUCTION OF THE MACHINE. 

(4.) The following data will also be given : 

Diameter of armature ; 

Weight of machine; 

Number of commutator bars ; 

Turns and length of wire in armature coils ; 

Whether brushes must be adjusted, or are automatic for different currents ; 
Diameter and length of bearings ; 

Number of turns per minute ; 

Number of volts for best work ; 

Number of amperes for best work. 



6 


SECTION III. 

PRELIMINARY TESTS. 

(5.) The resistance of the field magnet coils and of the armature coils 
will be measured as follows: A strong current from a secondary battery shall 
be passed through these coils and ampere-meter and sensitive voltameter used 
to determine current and fall of potential. The resistance will be determined 
from these measurements. As an additional precaution, a strip of german 
silver of known resistance shall have its fall of potential measured with the 
same current and instruments. These measurements shall be made before 
and after the tests, with the machine hot and cold. 

INSULATION RESISTANCE. 

(6.) Tests will be made of the insulation of the terminals of the machine 
from its metal bed-plate. 

Tests will be made of the insulation resistance between the commutator 
and the axle. 

(7.) It is understood between the parties that if any mechanical defect is 
observed, another machine may be substituted if the committee agree that 
such defect exists. 

The competitors shall have reasonable opportunity to obtain information 
of the progress of the tests, and to know the figures of each test for the object 
of ascertaining errors in time for correction. 

The observations made will be publicly posted before the machine is 
removed from the dynamometer. 

CALIBRATION OF INSTRUMENTS. 

(8.) The constants of all instruments used shall be determined by at 
least two independent methods. The companies shall have opportunity to 
inspect and observe the methods used and shall be furnished with the con¬ 
stants of the instruments immediately after they have been determined. All 
objections to the methods used will be received and acted upon as provided 
under Section IV., Article 17. 

SECTION IV. 

QUANTITATIVE TESTS. 

(9.) The dynamo to be tested will be run under full load for ten hours/ 
continuously, to see that all is in good working order before the tests begin. 

(10.) For the actual test the machine shall be run and the temperatures 
of the pole pieces and armatures observed until a uniform temperature is 
reached. 

(11.) When a uniform temperature for each load is reached, the measure¬ 
ments of power shall begin. 

(12.) The machine will be tested on both live and dead resistances. 

(13.) The machine will be tested on one-quarter, one-half, three-fourths, 
and full load. In the latter case, to be run at least five hours after a uniform 
temperature is reached. 


7 


(i4-) Full measurements of friction and of energy expended in field will 
be made in each case. 


DYNAMOMETRIC MEASUREMENTS. 

(15.) The shaft of the dynamo will be directly attached to the end of the 
shaft of Tatham’s dynamometer, by means of a universal joint coupling, and 
the horse-power used read from the dynamometer, unless the committee, for 
reason, shall decide otherwise. 

OBSERVATIONS. 

(16.) The observations on the dynamometer, current galvanometer, and 
potential galvanometer, and all other instruments, will be taken at synchro¬ 
nous intervals. 

The temperature of the room will be made as even as possible, and the 
temperature noted and necessary corrections made. 

The adjustment and oiling of machines shall be in the hands of the 
authorized expert for the company. 

(17.) In case any objection be made, or difference of opinion should arise 
between the committee and the contestants, the unanimous vote of the 
committee shall be final. 

If, however, there be not a unanimous vote, the minority of the committee 
shall appoint one referee and the majority another; these two shall appoint 
a third referee. 

The decision of the majority of these referees shall be final. 

In all determinations of efficiency of machines, measurement of potential 
shall be made (simultaneously with measurements of the current strength) 
at the binding posts of the machine, and at such other points of the circuit as 
will determine the total fall of potential, due to the resistance of the leads, 
connections and switches included in circuit with the instruments used for 
determining current strength. From these measurements, the loss shall be 
calculated and credited to the machine under trial. 

[Signed] Francis R. Upton. 

United States Electric Lighting Company , 1 
per Edward Weston, Electrician.) 


Plate I gives the general arrangement of the apparatus. The 
test room, in which most of the instruments for electrical meas¬ 
urement were placed, was in about the middle of the Exhibi¬ 
tion Building of the Franklin Institute. The dynamos, with the 
boiler and engine used in running them, were in a shed at one cor¬ 
ner of the building; and the resistances for their external circuit, 
—lamps and german silver strips—in a room inside the building 
and very near the shed. 



The storage battery, tangent galvanometer for current calibra¬ 
tions, and galvanometer for measuring field currents, were indif¬ 
ferent parts of the building, far enough from the test room not to 
affect the instruments in it. 

The leads from the dynamos and storage battery, and to the 
tangent galvanometer were of heavy, insulated copper cable. They 
were taken to the corner of the test house farthest from the instru¬ 
ments, and where they approached it the two parts of a circuit 
were twisted together, one of them being covered with rubber 
tubing as an additional precaution against leakage. Even with 
the heaviest currents (about 400 amperes) there was no effect on 
the instruments, and calibrations made both when the dynamos 
were and were not running, showed that any disturbance from 
currents in the leads had been avoided. 

Before any measurements were made, the insulation resistances 
between the leads themselves, and from the leads to the ground, 
were carefully tested and found in every case to be over fifty 
megohms; and measurements at intervals during the tests showed 
that they remained about the same 

OBSERVATIONS. 

The power applied to the dynamos was measured by a Tatham 
dynamometer, while the electrical energy was calculated from 
observations of the potential at the terminals of the machine, the 
currents in the external circuit and field, and the resistance of the 
armature. The latter was measured by sending a current from a 
storage battery through the armature and observing the current in 
the circuit and fall of potential between the terminals of the 
machine. 

The dynamos were run both on lamps and dead resistance, the 
value of the latter serving as a rough check on the potential and 
current. 


APPARATUS. 

Storage Battery .—This was kindly furnished by Mr. Weston, 
and was used for all calibrations, measurements of armature resist¬ 
ance, etc. Seventeen cells in series were generally employed ; 
they were placed on boards separated from the floor by porcelain 
insulators. 



Journal of the Franklin Institute, Vo/. CXX, 1885. 


Test a of Dynamo Electric Afuclures. 


Plate 1 


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Tangent Galvanometer .—This was used for calibrating the cur¬ 
rent galvanometer. It consisted of a single turn of large-sized 
wire fastened on the edge of a wooden disk which was nailed 
against a square board frame. The ends of the wire were bent up 
parallel to each other and fastened by brass connectors to the 
leads. A correction due to the space between the ends of the 
turn was applied to the mean radius. 

The diameter, about two metres, was measured in different direc¬ 
tions, and the mean taken in calculating the constant. 

There was a space cut in the middle of the wooden frame, with 
a shelf for the compass and needle. After the needle was adjusted 
to the centre and levelled, plumb lines and pointers were arranged 
so that any warping or change of level could be at once detected. 

The value of H was determined by a magnetometer of the Coast 
Survey pattern with detached theodolite ; it was found to be 

•1938 

and the constant of the galvanometer; 

31088 amperes. 

External Resistances of Dynamos .—The “dead” resistances for 
the external circuit of the dynamos were made of german silver 
strips 1*4 inches wide by about -oi inch thick. They were 
eight in number, each wound on a frame about 3 feet square 
by 10 feet high, made of four wooden uprights with pieces 
framed across at the top and bottom Porcelain insulators were 
fastened horizontally to the cross pieces and the resistances 
passed under one of the bottom insulators, over one at the top, to 
the bottom again, etc. Heavy copper wires were hard soldered to 
the ends of the strips and taken to the switch board. 

The resistances were adjusted by cutting out part of the strip 
by a short length of german silver with clamps at the ends, which 
could be shifted to cut out as many of the turns as was desired. 
The coils were adjusted by means of a calibrated bridge, to 2-400 
ohms at 20° C. There was a good air circulation in the room and 
fifty amperes could be carried by each coil. 

In the same room with the german silver resistances were the 
racks for the incandescent lamps used for “ live ” resistances. 

Switch-Board .—Two troughs about 2 y 2 feet long and I y 2 inches 
wide, and 10 inches apart, were cut in a heavy block of wood. 
Between them were bored two rows of eight holes each, and into these 


10 


were fitted glass insulators turned upside down to serve as mercury 
cups. The wood was soaked in boiling paraffine, and melted paraffine 
poured between the cups and allowed to harden. The distance 
between the troughs and the middle of the nearest row of cups was 
three and a-half inches; between the two rows, and the cups in each 
row, three inches. The cups and troughs were filled with mercury, 
heavy amalgamated copper rods in the latter serving to increase 
the conductivity. The resistances were brought to opposite cups 
in the two rows. 

The dynamo circuit was from one terminal of the machine to 
an ordinary Edison switch, by which the current could be made or 
broken, to one of the troughs; through the resistance to the other 
trough; to the test house, passing through the fixed resistance for 
current measurement there ; back by the other lead to the dynamo. 

Connections at the switch board were made by thick U-shaped 
copper rods, with a stretch of three and one-half inches. The 
resistances could be readily arranged in any desired way, with 
little or no chance of causing accident by making mistakes. The 
insulation between the troughs and the cups and the troughs 
themselves was practically perfect. 

Field Galvanometer .—The current in the field of the dynamos was 
measured by a tangent galvanometer of the Helmholtz type, the coils 
being each a single turn of large-sized wire. It was calibrated at the 
same time as the current galvanometer, being reversed as often as 
possible, and the same end of the needle read on each side of the 
zero mark. 

Wheatstone Bridge .—For measuring resistances that could not 
be taken to the Johns Hopkins University, a resistance box, with a 
bridge attachment by Elliott, of London, was used, with a Thomson 
astatic mirror galvanometer. The box was standardized, as de¬ 
scribed below. 

Calorimeter. —The calorimeter is shown in Figs, i and 2. 

This was used for calibrating both the potential and current 
galvanometers ; it was made of copper, was cylindrical in shape, 
about 8 inches in diameter by 10 inches in height, and held about 
eighteen pounds of water. 

The cover was screwed to a flange on the cylinder, the joint 
being water-tight; in it were holes with raised flanges around 


I 


them, for the terminals of the coil and the thermometer. For 
stirring, a shaft, working in a bearing on the bottom of the cylinder 
and passing through the cover, had on it five paddles arranged 
ak>ng its length and at different angles around it, and bent to throw 
the water past the wire out to the side of the vessel. On reaching 
the side, a downward motion was given to it by strips of light 
copper, making an angle of about 30° with the vertical, soldered 
to the cylinder and projecting inward one and one-fourth inches.. 
On the bottom of the shaft was a propeller blade. Putting saw-dust 
on the water and turning the shaft slowly showed the circulation, 
to be excellent. Turning the wheel belted to the pulley on the 
shaft three times per second, raised the temperature of the calori¬ 
meter -02° C. in five minutes. In the later experiments it was 
only turned once per second, so the error from this correction 
must have been small. 

In the first three experiments, copper wire of about 1*3 ohms 
resistance was used; in the last two, platinum-silver wire of 
I I ohms. The coil was held in the cylinder as follows: At equal 
distances around the cylinder, at the top and bottom, were 
soldered pieces of copper projecting inward, with clamps at their 
ends. The wire was wound on glass rods held in a light frame¬ 
work; the whole was placed in the cylinder, the rods clamped in 
place and the framework cut away, leaving a clear space lor the 
stirring arrangement. 

The terminals were small copper cups, thoroughly amalgamated 
and partly filled with mercury. They were surrounded by a rim 
of ebonite and wedged in their places in the cover. 

The calorimeter fitted in a light iron frame, from which it was 
separated by small blocks of ebonite. The whole was surrounded 
by a tin cylinder fitting closely on the shelf to which the frame 
was fastened, so there was no draught past the cylinder. 

Balances .—Two balances were used, one for weighing the calor¬ 
imeter, the other in voltameter work. The former could weigh up 
to thirty pounds and was very sensitive. The latter was an excellent 
analytical balance. Both were by Trcemner, of Philadelphia, and 
the weights were compared with standards in his possession. 

Thermometers. — The thermometers generally used were by 
Green, of New York. They were divided into degrees and tenths, and 
were compared at the Johns Hopkins University with one of the 


12 


standards there, the apparatus used in the comparison being that 
described by Professor Rowland, in his “ Determination of the 
Mechanical Equivalent of Heat.” * For the last two calorimeter 
experiments, a thermometer by Hicks, of London, was used. It was 
graduated to centimetres and millimetres, and was one of those used 
by Mr. Leibig, in his work “On the Variation of the Specific Heat 

of Water.” t 



fig. I. (Calorimeter, Fixed Resistance and Potential Resistance.) 


Potential and Current Galvanometers .—These will be described 
under measurements of potential and current. They, with the 
other instruments in the test house, rested on stone slabs cemented 
on the top of heavy wooden posts, sunk about two and one-half 
feet in the ground. 


* Proceedings of the American Academy of Arts and Science, 1880. 
f American Journal of Science, July, 1883. 
















































































































































13 




Fig. 2. (Test Room with Instruments in Position.) 



















































































































































































































































































































































































































































































14 


METHODS OF MEASUREMENT. 

MEASUREMENT OF RESISTANCE. 

For the standard resistance, a ten B. A. unit coil by Elliott, 
which had been compared at the Cavendish laboratory, and was used 
by Professor Rowland in his recent determination of the ohm, was 
employed. The values of the resistances in terms of this coil were 
reduced to the Paris ohm, by dividing by 

roi 12. 

The bridge used in the comparisons was built at the University 
Workshops, Cambridge, England. Its fixed (equal) arms were 
connected by a platinum-silver wire bent in a circle, and their ratio 
changed by making contact with the galvanometer circuit at 
different points on the wire. Beside the wire was a scale, and on the 
arm carrying the galvanometer contact, a vernier reading to tenths 
of a division. When the fixed coils were each one ohm, a whole 
division of the scale meant a change of one part in 10,000 of the 
ratio, while with the galvanometer used, a change of one-tenth of 
a division, or one part in 100,000 could be detected. The bridge 
had been calibrated for use in the determination of the ohm. With 
fixed coils of one ohm, the range of the instrument was about ten 
per cent, so the resistances to be compared were always approxi¬ 
mately equal. 

The different coils to be compared were balanced against resis¬ 
tances taken from “comparators,” designed by Prof. Rowland. 
Each of these consists of ten coils of equal resistance wound to¬ 
gether on a copper cylinder, the whole being coated with wax or 
paraffine and put inside a larger cylinder, the space between being 
filled with feathers. At the top, the cylinders are separated by an 
annular sheet of hard rubber,, around which two circles of ten 
holes each are bored for the terminals. The ends of each coil are 
taken to copper blocks screwed firmly beneath opposite holes in 
the two circles. The tops of the copper blocks are thoroughly 
amalgamated and the holes partly filled with mercury, connections 
being made by short U-shaped copper rods. 

Three comparators of ten, 100 and 1,000 ohms were used, giving 
a range of from one to 10,000 ohms. 

Each coil of the ten-ohm comparator was balanced directly 
against the ten-ohm standard, then the ten coils in series were 


5 


balanced against each of the ioo-ohm coils, and finally the ioo- 
ohm comparator in series compared with each of the i,ooo-ohm 
coils. In the measurements, the inner cylinders of the comparators 
were filled with water and the standard immersed in water, the 
temperatures being noted. 

The zero of the bridge scale was taken as the mean of the read¬ 
ings when the resistances being measured were reversed. 

In measuring the resistance boxes, they were kept for six or 
eight hours in a room whose temperature was nearly constant, 
and then balanced against corresponding resistances taken from 
the comparators, the temperatures being, of course, noted. 

The coil for potential measurement was immersed in turpentine, 
its temperature recorded, and its resistance measured as above. 

The resistances compared at the Johns Hopkins University were 
the box for current measurements, the coils and bridge for mea¬ 
suring resistance, and the coil for potential measurement. 

MEASUREMENT OF POTENTIAL. 

The galvanometer used for potential measurements was by 
Hartmann. It was furnished with a Siemens’ bell magnet, closely 
surrounded by a solid copper block, and damped very readily, only 
making two or three swings before coming to rest. The suspen¬ 
sion was a silk fibre about fifteen centimetres long. The coils, 
specially wound over the regular winding of the instrument, had a 
resistance of about two ohms. 

The galvanometer was in a circuit with resistances that were 
varied from 1,000 to 150,000 ohms, taken from boxes, two of 
100,000, one of 10,000 ohms, the former by Elliott and Breguet, 
the latter by Bergman. All calibrations being made with the 
(30,000 -j- 20,000) Elliott coils in the circuit, it was necessary to 
compare the other resistances with these coils. The arms of the 
bridge being made equal, the (30,000 -f 20,000) and (40,000 
-f- 10,000) Elliott coils were balanced in succession against the 
50,000 Breguet, resistances being added to one or the other until 
there was no deflection of the galvanometer. It was found that 
50,000 Breguet = (30,000 + 20,000 -j- 280) Elliott. 

50,000 Breguet = (40,000 + 10,000 -j- 250) Elliott. 

The (30,000 -j- 20,000) ohms Elliott was also measured in terms 
of the bridge coils, and the value found, 49,960, was so nearly 


i6 


correct that in getting the ratios of the 1,000 and 2,000 ohms 
Bergman—used in measuring armature resistance—to the (30,000 
_|_ 20,000) coils, it was assumed that their values in terms of the 
bridge coils were the same as if measured in terms of the 
(30,000 -j- 20,000) ohms. 

The deflections were read by a telescope and scale, the latter by 
Brown and Sharpe, graduated to centimetres and millimetres. 
The distance from the telescope to the mirror was two and one- 
half metres. 

Calibrations .—The galvanometer was calibrated, both by mea¬ 
suring a current passing through a standard resistance at whose 
terminals the leads of the instrument were connected; and by the 
difference of potential at the terminals of a calorimeter. The con¬ 
stant was also checked with that of the current galvanometer, after 
each test, by measuring the current through the german-silver strips 
used for the external circuit of the dynamos, and the potential at 
their extremities. 

During the tests,forty calibrations were made; thirty-six with the 
silver voltameter and standard coil, and four with the calorimeter. 
The constants determined by the calorimeter agreed so closely 
with the measurements by the voltameter, and the labor both of 
observation and calculation in the former was so much greater 
than in the latter, that it was thought unnecessary to make the 
observation any oftener. 

Voltameter Calibrations .—The current used varied from one to 
one and one-half amperes, giving a difference of potential at the ter¬ 
minals of the standard coils of from twenty to thirty volts. The 
coil shown in Fig. 1 was of No. 22 german-silver wire, wound on glass 
rods fixed in a wooden framework. The turns were kept apart by 
silk cord wound on the rods. The whole was immersed in a high grade 
oil (300° fire test) kindly furnished by the Standard Oil Company. 
The oil was constantly stirred while the current was passing. The 
measurement of the resistance has been described. Its value was 
21-161 ohms, at 14 0 C. 

For measuring the currents, a silver voltameter was used, the 
anode being a spiral of silver wire wrapped in filter paper, the 
cathode a platinum crucible filled with a 40 per cent, solution of 
silver nitrate The calibrations took from ten to twenty minutes, 
the deposit ranging from *9 gram to 2* grams. The times were 


noted by a chronometer whose rate, -f- I second per day, was 
neglected. 

When the experiment was finished, the solution was poured out 
of the crucible; the deposit first washed w'ith distilled water, then 
\ allowed to soak from one-hsflf hour to twelve hours, then washed 
again until there was no precipitate with a solution of sodium 
chloride, and finally slowly dried and then weighed. 

A double reading of the galvanometer was taken each minute, 
and the constant calculated from the mean reading for the time of 
observation. The constant is given by 




where 


k 50 == constant for (30,000 -f 20,000) ohms ; 

R = resistance of standard coil at 14 0 ; 

4 — temperature of standard coil; 

M c = temperature coefficient of standard coil; 

M h = temperature coefficient of box ; 

4 = temperature of box ; 

2 d = double deflection of galvanometer; 

25 0 being taken as the standard temperature of the box. 

When other resistances were used in the circuit, the constant 
was multiplied by their ratio to the (30,000 -f- 20,000) ohms. 

Calorimeter Calibrations .—rThe calorimeter has been described. 
In making the observations, the time the mercury crossed each 
half degree or centimetre of the thermometer was taken as 
the mean of the times of crossing the tenths before and after 
the division, and the division itself. In calculating the water 
equivalent of the calorimeter, the weight of the shaft was multiplied 
by the specific heat of steel; that of the cylinder by the specific 
heat of copper, and the weighf of the glass and wire, by their 
specific heat. For steel, the value of the specific heat was assumed 
to be 


•1110 

and that of copper 

•0940 

The principal correction to be applied is due to radiation. The 
other corrections are for rise of temperature from stirring, for the 

2* 



i8 


part of the thermometer stem in the air, and a small one for weigh¬ 
ing in air. 

The coefficient of radiation was determined by noting the rate 
of cooling, the calorimeter being slowly stirred. Experiments 
gave 

Difference between air and calorimeter, io° C. i coefficient, *00154 
“ “ “ “ “ 5 0 C. *00150 

“ “ “ “ “ o° C. *00149 

Before the experiments, and for the determination of the radiation, 
the cylinder was carefully polished. 

The correction for stirring was determined by bringing the 
calorimeter to exactly the temperature of the air, and then turning 
the wheel belted to the pulley on the shaft three times per second. 
The rise of temperature was *02° in five minutes. For the smaller 
velocity used in the later experiments, the heating was assumed to 
vary as the cube of the velocity. 

The correction for the temperature of the stem was taken from 

c = *000156 n {t — t") 

The following is one of the calibrations: 


Calorimeter Observations. Observers: i r 0 ’ 

l Duncan, June 20th, 11-40 A. M. 


Time of passing % 
Centimetre. 

Temperature of 
Calorimeter. 

Temperature of Air. 

Absolute Temperature 

of Calorimeter. 

Thermometers. 

3I-I98 

CM. 

17-50 

27- 

24-129 

For calorimeter, Hicks No. 108947. * 

32 - 35*7 

18- 

26-9 

24-826 

For air, Green No. 

33 - 5 2 -3 

18-50 

26*8 

25-523 


35 -° 8*3 

19- 

26-9 

26-221 

Water equivalent of calorimeter, corrected for weigh¬ 

36-23-8 

19-50 

26-9 

26-918 

ing in air 

37 - 4 i *3 

20 

27-0 

27-618 

= 8-4311 kilos. 

38-56-7 

20-50 

27*3 

28-316 

Value of mechanical equivalent used, (corrected for 

40-14-2 

21- 

27*4 

29-015 

Latitude) 

41-297 

2I-50 

27-6 

29*7 x 3 

= 425*75 

42-46-2 

22- 

27*7 

30 411 












19 


Current: Wyckoff Observer. • Potential: Murdock Observer. 


Deflec¬ 

tion. 

Remarks. 

Deflec- 
I ticn. 

Remarks. 

1 7 ’ 5 6 

>3 

II 

O 

IO27 

R = 50,000 

* 5 6 

4 23-0 

•26 

II 

to 

to 

0 

‘53 

4 22-40 

•26 


* 5 6 

h 24-0 

•26 


•54 


•25 


• 5 6 


•27 


*54 


•26 


•53 


•24 


'5 1 


•28 


.48 


* 2 £ 


* 5 ° 


•27 


•47 


•29 



In making the calculations, Rowland’s value of the mechanical 
equivalent was taken, because the thermometers used in the above 
experiment were compared directly with those employed by Prof. 
Rowland, and thus errors in thermometry were to a large extent 
eliminated. The following are the calculations for the observations: 


Interval. 

Corresponding 

In erval in Degrees 

Corresponding 
Interval of Time 

Degrees 
per Minute. 

Same Corrected 
for Radiation. 

centimetres. 

17-5 to 20 - 

3*489 

min. 

6 

sec. 

21 "5 

•5488 

•5473 

l8 tO 20*5 

3*490 

6 

21-0 

•5496 

•5490 

18-5 tO 21 ’ 

3-492 

6 

21-9 

•5486 

•5487 

19 to 21-5 

3-492 

6 

2i'5 

•5492 

•5502 

19-5 tO 22- 

3-493 

6 

22*5 

*5479 

•5497 





Mean: 

•54898 




































20 


•54898 
— -00044 
+ -00140 


Rise per minute, 

Correction for stirring, 

Correction for stem, 

Corrected rate, *54994 

C 2 R log, 9-517206 

R log, 9-038541 

C 2 log, -478665 

C log, *239332 

K c -02450 
^50 *1847 @22° 

Probably the greatest source of error in the calorimeter experi¬ 
ments was the superheating of the wire in the water. Using 
platinum-iridium wire varnished, with a smaller current than was 
generally employed in these experiments, Mr. L. B. Fletcher 
calculates * that the superheating is about 2° C. But in the 
measurements described above the wire was bare and the flow of 
water past it very much faster than in Mr. Fletcher’s work. In 
the last two experiments a rise of 2° C. would cause an error of less 
than one-tenth per cent., so it is probable that they are not much 
affected by this source of error. 

It is also possible that there was conduction through the water. 
The calorimeter was carefully cleaned before each experiment and 
distilled water used. If such an effect existed, it would be in an 
opposite direction from the superheating. 

The usual range of temperature was io° C.; in the experiment 
given it was a little over 6°. 

Besides the regular calibrations, the constant was calculated 
after each test, from the potential at the extremities of the german 
silver “ dead resistance,” the current being measured by the current 
galvanometer, and the resistance measured by the bridge. The 
following partial list of calibrations excludes measurements made in 
this way. It includes the time during which most of the tests 
were made—from June I ith to June 23d : 


* American Journal of Science, July, 1885. 








21 


Date. 

Value of K50 

Constant Used. 

Method. 

June. 

at 25 degrees. 

• at 25. 


II 

1-845 

1-847 

Voltameter. 

II 

1-8465 

1-847 

Voltameter. 

12 

I -847 

1-847 

Voltameter. 

12 

1-847 

1-847 

Voltameter. 

13 

1-844 

1-844 

Voltameter. 

14 

1-842 

1-844 

Voltameter. 

l6 

I-843 

1844 

Voltameter. 

17 

1-843 

1-844 

Voltameter. 

18 

■' 3 - 

00 

1-844 

Voltameter. 

19 

1-8434 

1-843 

Calorimeter. 

19 

00 

I -»43 

Voltameter. 

20 

1-8485 

1-843 

Calorimeter. 

22 

1-843 

1-843 

Voltameter. 

23 

1-843 

1843 

Voltameter. 


For the Edison Nos. 5 and 10 dynamos, the potential galvanom¬ 
eter was in the same position as when used for the duration test of 
lamps, in a room at some distance from the test house. The constant 
as determined during the tests of these machines agreed closely 
with that used in the duration tests, which had but just ended. But 
when the instrument was removed to the test house, the constant 
began to vary, changing greatly from day to day, with sometimes 
a sharp change during the day. The Weston No. 7 M dynamo 
was tested on full load with the constant in this unsatisfactory 
state, and between the second and third tests there was a change 
of over one per cent. Although the number of calibrations made 
these measurements perfectly trustworthy, yet the labor and 
anxiety were both too great to be repeated with each test. 

So before the machine was run on the partial loads, the galvano¬ 
meter was taken to pieces, the coils rewound and soaked in 
paraffine, and the stand of the tube carrying the suspension more 
firmly secured. A beam, which pressed against the wooden pier, 
was also cut away. After this, the constant did not vary, the 
calibrations rarely differing more than one-tenth per cent, from the 
constant used. 













22 


MEASUREMENT OF CURRENT. 

The currents were measured by observing the ratio of the 
potentials at the ends of a fixed resistance when a known current 
and the current to be measured were passing respectively. To do 
this, the terminals of a circuit containing a galvanometer and a 
resistance box were permanently fastened to the extremities of the 
fixed resistance. A current was sent through the latter, and the 
resistance of the box adjusted until the proper deflection of the 
galvanometer was obtained; the current was measured by the 
voltameter, tangent galvanometer, or calorimeter, and the deflec¬ 
tion and resistance were observed. When any other current was 
to be measured, the box was changed until the deflection was 
about the same as before, and both the deflection and resistance 
noted. The thermometers used in getting the temperatures of 
the different parts of the circuit were those by Green, already 
described. 

The notation and formulae used are as follows: 

Let C' be the current used in calibration; 
r' be the resistance used in calibration ; 
d' be the deflection used in calibration ; 
t' B be the temperature of fixed resistance at calibration ; 
t' h be the temperature of resistance box at calibration ; 
t' g be the temperature of galvanometer at calibration; 

C" be the current to be measured ; 

r" be the corresponding resistance ; 

d" be the corresponding deflection ; 

t\ be the corresponding temperature of fixed resistance ; 

t" b be the corresponding temperature of the box; 

t" g be the corresponding temperature of galvanometer ; 

/ 0 be the standard temperature — 25° C.; 

Ug be the temperature coefficient for galvanometer circuit; 
u s be the temperature coefficient for fixed resistance and 
box; 

G be the galvanometer resistance ; 
k be the constant at 25 0 C. 

Then 

k = ‘ 1 + «. (t' s - y 

2^ [ g {i~«, («' g - / 0 yy + »•'{! + u a (<'„!- q | ] 




23 


C" = k 2 d" [l - U s (£" - o] [<? (1 + « g {t\ — Q ) 

r" (1 « a (£"„ - £„)J 

Calculations were facilitated by making tables of 
G [1 + Ug (t s -t 0 )\ 
for the different temperatures, of 

r M '+ % (<b —01 

for the different resistances that were to be used, and of 

1 u s (t a C) 

for the different temperatures of the fixed resistance. 

Galvanometer. — A mirror galvanometer, by Edelmann, of 
Munich, was used. It was furnished with a ring magnet damped 
by surrounding copper blocks. The suspension, originally about two 
feet long, was shortened to about seven or eight inches by a copper 
rod passing inside the glass suspension tube; there was no trouble 
from vibrations. The coils were movable on graduated bars, but 
for the tests they were clamped and their position never changed. 
The resistance of the coils, with the fixed resistance and the leads 
to it, was 

•3973 ohms, at 25 0 . 

This was taken as G in the formulae, and the temperature coefficient 
for copper used; the value of the german silver fixed resistance 
being only about -0004 ohms, and the rest of the circuit being 
copper. The galvanometer was read with a mirror and scale, the 
latter being of porcelain, graduated to centimetres and millimetres. 
The distance from the galvanometer was 2- 5 metres. 

Resistance Box .—The resistance box, by Hartmann, being open 
at both ends and having no paraffine on the coils, was very well 
fitted for its work. Its measurement has been described. 

Fixed Resistance —The details of the fixed resistance are shown 
in Figs, j, 4. and 5, which are respectively, a plan, side elevation, 
and end view. It is also shown in perspective in Figs. 1 and 2. It 
consisted of three strips of german silver, 4^ inches broad by -036 
inches thick, the ends hard-soldered into heavy copper blocks. 


24 




l '■ 



































































































25 


One of the blocks had a terminal piece 
cast on it that was bent to clear the edge 
of the tank in which the resistance was 
placed, and dipped into a mercury cup, 
to which one of the main leads was 
brought. From the other block, two 
copper rods passing between the strips, 
were bent over the edge of the tank and 
dipped with the other main lead into another mercury cup. The 
terminals of the galvanometer circuit were soldered into the copper 
blocks and remained permanent during the tests. The whole was 
put in a rectangular tank filled with the same kind of oil as was 
used for the potential resistance. 

Calibrations .—Calibrations were made by sending a current 
through the fixed resistance, measuring it, observing the deflection 
of the galvanometer and the resistance in its circuit, and noting 
the temperatures. The calibrations usually lasted ten minutes. 
The constant was calculated by the formula already given. 

Three methods of measuring current were used; the silver 
voltameter, tangent galvanometer and calorimeter. 

For the voltameter calibrations, a large platinum dish was used 
as cathode, a flattened spiral of silver wire wrapped with filter 
paper as anode, while a forty to fifty per cent, solution of silver 
nitrate was employed. With this strength of solution and with 
the usual current, about four amperes, the deposit was very regular 
and beautiful. It was treated as described under potential 
measurements. The resistance in the circuit was about ten ohms. 

The tangent galvanometer has been already described. Two 
observers read both ends of the needle on each side of the zero 
mark. The current was reversed every minute; it varied from 
twenty to thirty amperes. 

The method of using the calorimeter has been described The 
observations give C 2 R, and R being measured by the bridge, C 
may be found, with the advantage that errors of observation are 
halved in the value of C. 

Altogether, there were five calibrations by the tangent, nine by 
the voltameter and five by the calorimeter. The following are the 
values obtained : 



4 






















26 


•0245 io by voltameter. 

•024510 by voltameter. 

•024440 by tangent galvanometer. 

•0245 50 by tangent galvanometer. 

•024510 by voltameter. 

•024480 by voltameter. 

•024590 by tangent. 

by calorimeter. 

•02455 by tangent. 

•02455 by voltameter. 

024481 by calorimeter. 

•024477 by calorimeter. 

•024520 by tangent. 

•024500 by voltameter. 

•024516 by voltameter 

•02453 by calorimeter. 

•024495 by voltameter. 

•024494 by voltameter. 

•02450 by calorimeter. 

This principle of measuring current has been used before, 
notably at the Vienna and Munich Exhibitions, but as employed 
in the following tests the method differs from that previously used 
in an important particular, i. e., the construction of the fixed 
resistance. The substitution in the fixed resistance of german 
silver strips in oil instead of the copper bars in air formerly em¬ 
ployed, increased greatly both the range and accuracy of the 
method. 

As the method has not been commonly used, and is possibly not 
very generally understood, a brief discussion of the sources of 
error and their probable value in these tests will be given. 

The possible sources of error are : 

(1.) In observing the deflections; 

(2.) In the constant; 

(3.) In the temperature correction for fixed resistance ; 

(4.) In the temperature correction for resistance box; 

(5.) In the temperature correction for galvanometer ; 

(6.) In the values of the coils in the box; 

(7.) In the resistance of the galvanometer coils; 

(8.) In assuming the currents proportional to 2 d. 


27 


(/ ) Error in observing the deflections. 

This error would enter directly in the result. The scale could 5 
be read with considerable accuracy to tenths of millimetres; the 
double deflections were usually between twenty and thirty centi¬ 
metres. The currents measured were quite steady, but even if 
they varied, the excellent damping of the galvanometer would* 
allow the readings to be taken with a good deal of precision. 

(. 2 .) Errors in the constant. 

On looking at the table of constants, it will be seen that the 
results obtained with different resistances in the galvanometer cir¬ 
cuit, different currents, temperatures and deflections, and by 
entirely independent methods of measuring current, agree so 
closely that their mean must be very near the true constant. Two- 
of them, exceptional ones, differ from the mean by one-third per 
cent., a few more by one-sixth per cent., but the greater number 
are within one-tenth per cent, of the constant used. Double 
weight was given the voltameter calibration, as involving less pos¬ 
sibility of error than the other methods; with two exceptions, they 
are within one-fifteenth per cent, of the mean. Any error would 
enter directly. 

(j.) Errors in the temperature correction of the fixed resistance. 

The uncertainty due to the temperature correction of the fixed 
resistance must have been inappreciable. Its temperature coeffi¬ 
cient was small, about one-tenth that of copper, while its tempera¬ 
ture, considering the large surface of very thin metal exposed to 
the liquid, must have been quite accurately known. For the 
heavier currents, the oil was constantly stirred. With about 400 
amperes in the circuit, the thermometer registered -i° C. more 
when held against the strip than when in the body of the liquid 
while the oil rose 1-5° during the test. To further decrease the 
possibility of error, the oil was kept within at the most 5 0 or 6° of 
the usual temperature of calibration by cooling it when necessary 
between the tests. An error would enter directly in the results. 

(4.) Errors in the temperature correction of the resistance box. 

Both ends of the box were open to the air and the coils were 
not coated with paraffine. The bulb of the thermometer lay against 
or very near the coil in use. The currents could cause no appre¬ 
ciable heating and the temperature of the room changed slowly. 


28 


The temperature coefficient was taken as 

•0004, 

and calibrations made at different temperatures showed that this 
was not much in error. Errors would enter almost directly in the 
result. 

(5.) Errors in the temperature correction of the galvanometer 
coils. 

The temperature of the galvanometer coils was given by a 
thermometer hung near them. With the smallest resistance used, 
any error in this correction would only enter as one twenty-fifth 
in the result. 

(d.) Errors in the values of the coils in the resistance box. 

The measurement of the resistance box has been described. The 
values were probably correct within one part in 2,000 or 3,000. 
Any error would enter directly in the result. 

(7.) Errors in the resistance of the galvanometer circuit. 

The resistance of the galvanometer and its circuit was measured 
by the standardized bridge. The error was probably small and 
entered at the most as one twenty-fifth in the result. 

(<?.) Error in assuming the currents proportional to 2 d. 

This error is slight and was to a large extent eliminated by 
making the calibration on about the same part of the scale as the 
measurements. 

The only errors then that would be appreciable are in the deflec¬ 
tions, the constant, the temperature correction of the box, and the 
values of the resistance coils. The last of these could hardly have 
been over one-twentieth per cent.; the temperature correction of 
the box was probably within one-tenth per cent. 

This method has several advantages. The range is very great 
(with the apparatus described currents of from two or three amperes 
to 400 could be measured with about the same accuracy) while the 
errors are not multiplied in the result and are of such a nature that 
with proper precautions many of them can be almost entirely 
eliminated, and the rest made very small. 

Although in measurements of both potential and current any 
change in H would directly affect the results, yet as certainly two 


29 


and usually more voltameter calibrations were made for each day 
of the tests, and the constants were checked after each measure¬ 
ment, it is not probable that any important error arose from this 
cause. 

It is also interesting to note that the magnetometer records 
that showed such irregularities during the life test of lamps* 
just finished, were remarkably uniform during the dynamo tests. 

POWER MEASUREMENTS. 

The general principle of the Tatham dynamometer is shown in 
Fig. 6. The power applied to the shaft on which the driving 
pulley D is fixed, is transmitted to the pulley B, to whose shaft the 
machine to be tested is coupled, by an endless belt, which passes 



over D, under the stretching pulley 5 , over the weighing pulley 
W, under B, over the second weighing pulley W } under S, back to 
the place of starting. Each of the weighing pulleys W is sup¬ 
ported in a cradle, the outer end of which is pivoted on the knife 
edge F f while the inner end is supported by the link L C. The 
upper ends of the two links are fastened to the scale beam F f P at 
equal distances from and on either side of the fulcrum F. 

To calculate the power applied to the pulley B, it is necessary 
to know three things : The difference of tension of the belt on the 
two sides of B; its effective diameter, and its number of revolu¬ 
tions. These will be discussed in order. 

The scale beam is acted upon through the links L C, fastened 


* Journal Franklin Institute, Sept., 1885. 













30 


to the cradles of the weighing pulleys W. The tensions of the 
belt on the outer faces of these pulleys have no effect on the 
beam, since the line of effort of the belt passes through the knife 
edges F. The only forces then that act on the beam are the two 
tensions of the belt on the inner faces of the pulleys W, and these 
are the tensions on the two sides of B ; and the links being at equal 
distances on either side of F t the difference of the tensions is 
recorded on the beam. 

The scale beam was of steel, graduated by Brown and Sharpe 
into 600 divisions. With the weight used each division meant 
one-half pound. A small poise travelling on the weight allowed 
readings to be taken to ^-^th °f a pound. 

There were two adjustments to the cradles. In the first, the 
axis of the pulley W was moved by micrometer screws to such a 
position that the line of effort of the belt passed through the knife 
edges of the cradle. To show this, the pulley was chocked, a short 
piece of the belting hung on its outside face, and weights placed 
in a pan hanging to the belt. When there was no effect on the 
scale beam, the adjustment was accomplished. 

The second adjustment determined the position of the knife 
edge to which the links were connected. This was moved until 
the beam weighed about 250 pounds correctly to within one- 
twentieth of a pound. 

The pulley B was calculated to deliver 6-6 feet per revolu¬ 
tion, but the belting used was thicker than was at first intended, 
and the value 6-6 should be increased by one-fourth per cent, The 
effective diameter of the pulley, including the thickness of the belt, 
was measured directly, and also calculated from the length of 
belt delivered by five turns of the pulley. For the latter measure¬ 
ment, two steel points, one of which was fitted with a micrometer 
screw, were fixed on a wooden rule, and their distance apart 
accurately determined on a standard scale. Marks were made on 
both the pulley and belt opposite to fixed pointers. Five revolutions 
were given the pulley, and the length of belt that passed the 
pointer was measured by the rule with the steel points, any margin 
being taken off by a pair of compasses. The pulley was turned 
both ways and the effect of stretching eliminated. 

The two methods checked very closely, and gave for the delivery 
of the pulley 


6 6 (1-0025) feet per revolution. 


3i 


A very ingenious mechanical counter registered the number of 
revolutions. Observations could be taken each minute, and the 
counter recorded continuously to 1,000,000 revolutions. 

Having the difference of tension on the two sides of B , its 
delivery per turn, and number of turns per minute, the horse¬ 
power is calculated as follows : 

Horse-power = divs. scale beam X no. revs. X — - ^ 002 ^ 

2 X 33000 

Horse-power = 1-0025 ' di vs. scale beam X no. turns per min. 1 

I 10,000 ) 

It will be seen that the only part of the friction of the dynamom¬ 
eter that appears in the readings, is that due to the bearings of the 
pulley B. By the principle of Morin, that the sum of the tensions 
on the two parts of a belt is constant, this friction should be the 
same whatever the load. In getting the power applied to a 
machine, after the measurements have been made with the 
machine coupled to the dynamometer, it was uncoupled and the 
■dynamometer run at the same number of revolutions, the scale 
beam observed, and its reading subtracted from the reading when 
coupled. 

To avoid the uncertainty of loss due to belting, the shaft of the 
driven pulley i? was coupled directly to the dynamo by a universal 
coupling, as shown in Fig. 7. It was assumed that this would 
allow for any slight inexactitude in lining the dynamo and dynamo¬ 
meter shafts, but it is'doubtful if it was of much value at the high 
speeds used for the tests. 

The figure of the dynamometer [See Frontispiece) gives a view of 
it as used in these tests. The automatic recorder for the scale beam, 
shown in the figure, was not used. In making observations, the num¬ 
ber of revolutions and scale beam were read each minute, usually for 
ten minutes. The means of the two sets were multiplied together, 
the product divided by 10,000, and a correction of one-fourth per 
cent, applied, as given in the formula. 

The delicacy and range of the dynamometer were both very 
great. On one occasion the power absorbed by a single Weston 
mammoth lamp was accurately measured, while the slightest varia¬ 
tion of the load could be at once detected. During a test, the 
scale beam usually floated steadily, the slight and rapid jar caused 




32 


by running served to limber up the weighing apparatus and render 
it especially sensitive. Indeed, it would be hard to fix a limit to the 
accuracy with which the observations could be taken. 



Mr. Tatham has published a paper,* giving the principles 
involved in the dynamometer, and describing its various modifica¬ 
tions of form. 

The engine used was a io" x 20" Salem Buckeye. Its governor 
adjustment could be readily varied from 100 to 200 revolutions. 
The speed, under the steady load of a dynamo, was very uniform. 

A steel boiler, loaned by the Baldwin Locomotive Works, was 
used. It could safely carry 150 pounds per square inch and 
develop eighty horse-power. 


* Journal Franklin Institute, Dec., 1882. Vol. cxiv. 

































































33 


CHECKING THE DYNAMOMETER. 

In order to make the tests absolutely, as well as relatively 
accurate, it was decided to check the work recorded by the 
dynamometer against an amount of work calculated from the 
mechanical equivalent of heat. 

To do this, a calorimeter was constructed, the general plan of 
which is shown in side and end section in Figs. 8 and p. 




It was of wrought iron, 3 feet long by 3 feet in diameter, with 
V-shaped projections riveted inside the shell. The paddles, 30 
inches long by y 2 inch thick, were keyed to the shaft and moved 
between the V’s. One end of the shaft passed through the end of 
the calorimeter, and was coupled to the dynamometer. In the 
experiments but one paddle was used, 700 revolutions absorbing 
about forty-five horse-power. 

Two different methods of experiment were employed; first, 
with a constant weight of water and an increasing temperature; 

3 * 







































34 


and second, with a constant temperature and a continuous flow of 
water through the calorimeter. 

First Method .—In the first method, the calorimeter was filled and 
its water equivalent found, the engine was then started, and the rise of 
temperature noted and the dynamometer observed. The mechanical 
equivalent was calculated from the work recorded by the dyna¬ 
mometer, the water equivalent of the calorimeter and the rise of 
temperature, the necessary corrections being applied to the latter. 
The value thus obtained was compared with the values of Joule 
and Rowland. 

In getting the water equivalent, the calorimeter was first 
weighed empty and then when filled with water. The difference 
gave the weight of the water, and the water equivalent of the iron 
was calculated from its weight and specific heat. It was intended 
to determine by experiment the specific heat of the specimens of 
the iron used.in the calorimeter, but circumstances made this 
impossible. The value used, 


*112, 

is taken from determinations by Bystrom, Weinhold, Regnault 
and Bede, reduced to 30° C. The values given by these different 
experimenters agree very well, and it seems probable that the 
mean does not differ from the specific heat of the iron used in the 
calorimeter by more than one or two per cent, at the most—an 
error that enters as about one-tenth in the result. 

The weighings were made with a scale beam by Fairbanks. 
Both the weights and graduation had been tested. 

The following are the results obtained: 

Weight of calorimeter alone, 122875 pounds. 

Weight of calorimeter with water, 245175 pounds. 
Weight of water, 12230 pounds. 

Water equivalent of the iron, 137-62 pounds. 


Total water equivalent, 1360 62 pounds. 

Correction for weighing in air, 138 pounds. 

Water equivalent, corrected, 1362-00 pounds. 

Temperature Observations .—The thermometers used were those 
by Green, already described. The time the mercury crossed each 
half degree was observed and was taken as the mean of the times 
of crossing the tenths below and above the division, and the divi¬ 
sion itself. The times were noted by a chronometer. 



35 


The following table gives the temperature observations and the 
dynamometer readings,—the latter were taken each minute : 

Calorimeter Observations for Checking Dynamometer , June 27. 


Temperature. 

Observed Time 
of Crossing 
Division. 

Corrected Time 
of Crossing 
Division. 

Intervals for 
4 - 5 ° C. j 

Remarks. 

30 5 

12-01-44- 

12-01-44- 


The times were correct¬ 

31 ' 

02-20 3 

02-20-3 


ed arbitrarily by the obser¬ 

31-5 

02-57-0 

02-56 8 


vations on either side. 

3 2 ' 

03 - 33-3 

03-33 3 



32*5 

04-09-6 

04-09-7 



33 ’ 

04-46-0 

04-46-3 



33*5 

05-22-3 

05-23 -1 



34 * 

06- i-6* 

06^-00-2 



345 

06-37-6 

06-37-3 



35 * 

07-140 

07-14-4 

5 - 30-4 


35*5 

07-51-6 

07-51-6 

5 - 31-3 


36- 

08-29-0 

08-290 

5 - 32-2 


36-5 

09-07-3 

09-06-2 

5-32-9 


37 * 

09 - 43*3 

09-434 

5 - 33-7 


375 

10-20-3 

10-20-6 

5 - 34-3 


38 ' 

10-580 

10-5 80 

5 - 34-9 


38-5 

11-36-0 

ii -35 5 

5-353 


39 * 

12-13-0 

12-130 

5-357 



*Untrustworthy, only one reading. 

Dynamometer Readings. 


Time. 

Counter. 

Scale Beam. 

Friction. 

Remarks. 

12-01-00 

02-00 

0159 

0881 

665 

I372 


03-00 

1603 

666 

13-72 


04-00 

2326 

664 

I372 


05-OO 

3042 

661 

13-72 


06-00 

3761 

661 

1372 


O7-OO 

4479 

661 

I 3-72 


08-00 

5198 

66 3 

1372 


09-00 

59 i 6 

666 

I372 


10-00 

6640 

666 

I372 


11-00 

7360 

666 

13-72 


Mean : 

720-1 

6639 

I372 



The corrections to be applied to the thermometer readings are 
for the part of the stem in the air, and for radiation. The first 
of these is somewhat indefinite, as a portion of the stem is heated 
























36 


by conduction from the calorimeter. The whole correction, how¬ 
ever, is only about one-third per cent., and its value is probably 
correct within twenty or thirty per cent, so the error in the result 
from this cause can hardly be much over one-tenth per cent. 

But the most important correction, and the one in which there 
seems the greatest possibility of error, is the coefficient of radia¬ 
tion. This is usually determined by slowly stirring the calori¬ 
meter, and noting its difference of temperature from the air and 
rate of cooling, correcting for the heat developed in stirring. But 
with a single thin blade, and no arrangement for causing circu¬ 
lation, this method was impracticable. In some experiments that 
were tried, the water was not thoroughly mixed, and the cool 
water falling and warm water coming to the top, made the values 
obtained worthless. 

Under these circumstances, it became necessary to calculate 
the radiation from the experiment for the determination of the 
mechanical equivalent. 

The method of calculation was as follows: The observations 
were divided into intervals of 4-5° C., as shown in the following 
table, and the corresponding intervals of time were reduced to the 
same rate of doing work, the same value of the specific heat of 
water, and the same value for the stem correction of the ther¬ 
mometer. The remaining difference in the intervals is assumed 
to be due to radiation. 


Calculation of Radiation. 


Interval. 

Time Interval 
Uncorrected 

Ratio of Rate of 
Doing W ork to 
Mean Rate. 

Correction for 
Specific Heat of 
Water.* 

Correction for 
Stem 
in Air.* 

Time Interval 
Corrected. 

Excess over 

First Interval. 

degrees. 

minutes. 

X 


-f- 

minutes. 

minutes. 

3°'5 35' 

5 5067 

I '00145 

1 '00000 

1 00000 

5'5J467 

•ooooo 

3 1 ' — 35'5 

5'5217 

I'00026 

1 00000 

1 '00016 

552224 

•00757 

3 i '5 — 36 ■ 

5'5367 

'99957 

I’OOOIO 

1 -00032 

5-53200 

•QI733 

3 2 ' —365 

5 5483 

•99885 

1*00020 

1*00048 

5 54i9 6 

'02729 

3 2 'S—37‘ 

5'56i7 

•99847 

I (-0031 

1'00065 

5 54808 

■°334i 

s 33‘ —37'5 

5'57 r 7 

•99824 

I '00040 

1*00081 

5'55536 

'04063 

33'S—38 0 

5'58i7 

'99980 

I '00050 

1 00097 

5'5725o 

05783 

34’ —38-S 

5:5883 

1'00134 

I '00060 

x'00113 

5-58607 

•O7I4O 

34-5—39' 

5 595° 

1 00219 

I '00070 

1'00130 

5-59600 

•08133 


Gives radiation '00258° per degree per minute. 

* These are the ratios of each succeeding interval to the first interval. 












37 


The differences of these corrected intervals from the first 
interval were plotted, the excess of the mean temperatures of the 
intervals over that of the air being taken as abscissas, and the 
above differences as ordinates. A straight line was drawn through 
the points thus found. The radiation was calculated by taking 
the difference of the ordinates for an interval of 4 0 , and from this 
value (which is the loss of time due to radiation, in an interval* of 
about 5-55 minutes, the difference of temperature being 4 0 ), the 
coefficient of radiation was easily found. 

In drawing a straight line through the points, we have assumed 
the coefficient of radiation to be constant when the excess of tem¬ 
perature over that of the air varies, instead of increasing with the 
excess. Within the rather narrow limits of temperature used, 
however, the value found represents very nearly the radiation for 
the mean interval. In calculating the experiment by the second 
method, the value of the radiation found above was corrected to 
the greater difference of temperature between the calorimeter and 
air, by increasing it in the ratio shown by the experiments of 
McFarlane and Rowland 

This method of calculating the radiation, while not so accurate 
as the method usually employed, has the advantage that the con¬ 
ditions of observation are accurately those of the experiment to 
which the radiation is applied. 

It will be seen that the errors likely to affect the radiation 
coefficient, are errors of observation, in the relative values of the 
specific heat of water at the different temperatures, and in the ratios 
of the stem corrections. 

As for errors of observation, the dynamometer readings for the 
intervals were the mean of five observations, and, although the 
jar interfered somewhat with the readings of the thermometer, yet 
the table shows that there were no very great errors, and the 
method of observation allowed the readings to be to some extent 
corrected by those on either side. 

The ratios of the values of the specific heat of water for the 
different intervals were calculated from Rowland’s values of the 
mechanical equivalent for the mean temperatures of the intervals. 
Fortunately the correction was small, and probably accurately 
given. 

Whatever the absolute value of the stem correction might have 


3« 

been, there could be little error in the relative values for the dif- 
ferent intervals. 

The result obtained was: 

Excess of cal. over air, 4 0 C. coefficient of radiation, *00258 

go *00262 

On applying the above values to the observation by the first 
method, we obtain : 

Mean rise of temperature, per minute (uncorrected) *809814 
Mean correction for radiation, 4" *° T 779° 

Mean correction for stem, + *003034 

Mean correction to absolute temperature, — *001350 


Mean rise, per minute (corrected) 

Water equivalent of calorimeter, 
Heat units developed, per minute, 


•822288 

1362*0 pounds. 
1119*9562 


Mean reading scale beam, 
Friction reading scale beam, 


663*9 

13*72 


Difference reading scale beam, 

Mean revolutions, 

Work in foot pounds = product 

Mechanical equivalent for i° C, 
Mechanical equivalent for i° F., 


65018 

720*1 

X 3‘3 X 1-0025 15489048 

1383*01 ft. lbs. 
768*34 ft. lbs. 


Unfortunately, however, the construction of the calorimeter 
made the results of this experiment untrustworthy. The blades 
were kept apart by pieces of 4-inch pipe, inch thick, fitting over 
the shaft between them. In the space between the shaft and pipe 
were about five pounds of water not in circulation with the mass 
in the calorimeter. The shaft being jacketted with this layer of 
water, must have gained heat but slowly. The result was that the 
heat units calculated were too great, and the mechanical equivalent 
too small. It is also probable that this effect would make the 
coefficient of radiation calculated from this experiment slightly too 
large. 

We can only say of this experiment then that the value is 
768*3 4^ an indeterminate correction. 




39 


Second Method .—In this method water was made to flow continu¬ 
ously through the calorimeter. The engine was run until the tempera¬ 
ture of the exit water ceased to rise, and then observations of the 
entrance and exit temperatures and of the dynamometer were taken 
each minute, and the exit water weighed every four minutes. The 
weighings were made by two of Fairbanks’ platform scales that had 
been tested with standard weights. The observations lasted one and 
one-half hours. The heat units were calculated for each interval 
of four minutes, as shown in the table, and their sum taken for the 
w.hole interval. The scale reading and number of revolutions of 
the dynamometer were averaged for the time of the experiment, 
the work being calculated from the means (Philadelphia time). 


40 


Continuous Calibration .— Tatham Dynamometer , June 27 , 1885. 


Time. 

Mean 

Temperature 

Exit. 

Mean 

Temperature 

Entrance 

Increase. 

Weight H 2 0 

Heat Units. 

11 *02 

*o6 

39*528 

23*82 , 

15708 

287*25 

45 I 2 *I 23 

*IO 

39*5975 

23*8225 

15*775 

267*00 

4211*925 

*14 

39*65 

23*8125 

15*8375 

261*25 

4 I 37-546875 

*18-30 

397125 

23 - 8 I 5 

15*8975 

293*75 

4669*890625 

•22 

397025 

23*82 

15*8825 

235*00 

3732'3875 

*26*30 

39' 6 7 

23*8025 

15*8675 

3 I0 * 5 0 

4926*85875 

•30 

39’ 6 45 

23*80 

15*845 

228*75 

3624*54375 

'34 

39*6125 

23*80 

15*8125 

271*25 

4289*140625 

'38 

39*6150 

23-805 

15*810 

274*00 

4331*94 

•42 

39‘5875 

23*8025 

15*785 

270*75 

4273*78875 

•46 

39'5875 

23’8275 

15*76 

274*00 i 

43 l 8*24 

■50 

39*5375 

23-845 

15*6925 

276*00 

433 I*I 3 

'54 

39*52 

23-8525 

15*6675 

275*00 

4308*5625 

•58 

39'485 

23*84 

15*645 

276*00 

4318*02 

12*02 

39*4450 

23*84 

15*605 

277*75 

4334*28875 

•06 

39*342 5 

23*85 

15*4925 

289*00 

4477*3325 

*IO 

39* 2 55 

23*86 

15*395 

286*25 

4406*81875 

•14 

39*1425 

23*8825 

15*26 

287*00 

4379*62 

*l8 

39*0775 

23*8925 

15*185 

28475 

4323*92875 

*22 

39*01:25 

23*90 

15*1125 

284*00 

4291*95 

*26 

38*98 

23*91 

15*07 

289*25 

4358-9975 

•30 

38-895 

23*91 

14-985 

287*50 

4308*1875 

'34 

38-865 

23*91 

T 4*95 5 

290*50 

4344*4275 

■38 

38-78 

23-905 

14*875 

293*50 

4365-8125 

•42 

38-8175 

23-9I5 

14*9025 

275*50 

4105*63875 

•46 

38-93 

23*925 

15*005 

272*25 

4085*1 I 125 

•50 

39*04 

23*925 

15*115 

270*50 

4088*6075 

'54 

39*175 

23-94 

1 5*235 

265*50 

4044*8925' 

•58 

39*3475 

23*925 

15*4225 

263*50 

4063*82875 

1*02 

39*4o5 

23*9 1 2 5 

15*4925 

271*00 

4198*4675 

*06 

39*45 

23-9025 

15*5475 

273*25 

4248*354375 

1*10 

39*4825 

23-90 

15*5825 

272*50 

4246*23125 

•14 

39*485 

2392 

15*565 

273*00 

4249*245 

•18 

39'4925 

23*92 

i 5*5725 

268*00 

4173*43 

*22 

39*525 

23-905 

15*62 

267*50 

4178-35 

*26 

39 ' 5 i 

23 * 9 ° 

15*61 

274-75 

4288*8475 

•30 

39*52 1 

23*895 

15*625 

268*00 

4 I 87-5 

Total number heat units, 

.... 


I 57735*96550 



































4 


When the experiment was finished, the two cocks on the calori¬ 
meter were closed, and the engine stopped. The temperature of 
the water was then found to be 39 0 . The time occupied in 
stopping was about four minutes, equivalent to two minutes on full 
load. From the data of the previous experiment, the rise of 
temperature would be about -85° C. per minute, and therefore the 
average temperature of the calorimeter during the second experi¬ 
ment was about 37*3°. 

From the above table and the dynamometer record, we get the 
following data: 

Mean reading scale beam, 655-9195 

Mean friction reading, 13 72 


Corrected reading, 642-1995 

No. revolutions, 106,180 

Foot pounds absorbed, 225585395- 


Heat units passing through cal. (uncorrected,) 

157735-96 

Heat units radiated from calorimeter, 

+ 4045-89 

Correction to reduce ther. to abs. temp., 

— 169-63 

Stem correction, 

+ 647-12 

Total heat units, 

162169-34 


Mechanical equivalent for i° C., 1391 05 foot pounds. 

Mechanical equivalent for i° F., 772-81 foot pounds. 

In this method the uncertainty due to the specific heat of the 
iron, and its temperature is avoided. The greatest possibilities of 
error are in the mean temperature of the calorimeter and the stem 
correction. It is probable that too great a value of the latter has 
been taken; for the thermometers were in the water for several 
hours and a considerable portion of the stem must have been 
heated by conduction. 

The coefficient of radiation was taken from the first experiment. 

The results of the experiments are : 

First method mech. equiv. = 768-3 an indeterminate correction 
Second method mech. equiv. — 772-81 

It would seem then that within the limit of error of these 
experiments, the dynamometer is correct, and, considering the 
probable accuracy of the last method, there seems little doubt that 
the work calculated from the dynamometer readings is as accurate 
as the adjustments of the machine and the readings themselves. 




42 


TESTS. 

For the full load tests, the machines were run at least ten hours 
before any measurements were made. They were then tested at 
intervals of from one to two hours. 

For the partial loads, the dynamos were run on quarter load 
for two or three hours, then tested, then run on half load for a 
couple of hours, and tested, etc. 

The metho.d of making a test was as follows : A time to begin 
was set, and the observers got ready to start at the signal from 
the test house. After the signal, double readings of the potential 
and current galvanometers were simultaneously made each minute, 
and the scale beam and number of revolutions of the dynamometer 
observed. The field galvanometer was reversed, and read as often 
as possible, usually four or five double readings. 

At the end of ten minutes, a signal to stop was made; the 
dynamo was stopped, the field circuit broken, the storage battery 
put on, and the armature resistance measured. The brushes were 
then lifted, and the field circuit made and its resistance measured. 
Finally, the constants of the current and potential galvanometers 
were checked on the german silver strips. 

When the tests for the day were finished, the friction of the 
armature and of the dynamometer were obtained, and the latter 
subtracted from the power applied for each test. 

Communication from the test house to the dynamo shed was 
by an electric bell, and through a speaking tube. 

The following notation will be used in the formulae : 

e difference of potential between terminals of dynamo; 

E total electro-motive force generated in armature ; 

i current in external circuit; 

4 current in field ; 

R resistance of external circuit; 

r a resistance of armature coils; 

r s resistance of field with box for adjustment; 

5 resistance of field alone ; 

W energy applied in horse-power ; 

W t total electrical energy in horse-power ; 

W e energy in external circuit in horse-power; 

W & energy in armature in horse-power ; 


43 


W s energy in field in horse-power ; 

E/ t total efficiency of electrical conversion ; 

E/ c useful commercial efficiency ; 

5 ? = E fz/Efl\ 

/ a percentage of power used in armature; 
p s percentage of power used in field ; 
n number of revolutions per minute ; 

Fric. friction of armature ; 

4 temperature of the air in degrees centigrade; 

4 temperature of pole-piece in degrees centigrade ; 

Of these, e t i, 4, r a , S, W , n , 4 and 4 were observed directly. 

E was calculated from 5 = e -f. ( i + 4 ) r & J 
7 ? was obtained from R == <? / z; 

74 was from r s = e/i s ] it was also checked by observatio 
after each test. 


The other formulae used were 

yy __ (} +4) e + (4 + 

4 745 3 


4) 2 ^a 


H4 = 
W s = 
Wt = 

v = 

p* = 


745*3 


(* + M 2r « 

745-3 

4 ^ 

Tf 

W 

Ef c 

Wt 

w 


- 

Ps w 






44 


EDISON NO. 5 DYNAMO. 

Diameter of armature, 7 ^" inner; 71 /% 

Weight of machine, 2 475 pounds. 

Number cf commutator bars, 50 

Turns of wire in a coil. 2 

Length of useful wire in a coil, 52" 

Brushes adjusted or not? • yes. 

Diameter of bearing, 

Length of bearing, 5^ 

Revolutions per minute, 1400 

Volts for best work, 125 

Amperes for best work, 100 

Table 1 gives the result of the measurements: 


\J>J 
1 6 


outer. 


45 


Table I. — (Edison No. 5 Dynamo.) 


Date. 

May 29th. 

Time, 

12-40 

1 

1-40 

3-00 

Load, 

Full. 

Full. 


E. M. F. at terminals, . 

125-2 

121-59 


Total E. M. F., . . . . 

I 3 I -5 

128-00 


Current in ext. circ , . . 

IOO 92 

98-06 


Current in field, .... 

00 

2-296 


External resistance, . . 

I ’ 2 4 I d 

1-240a 


Armature resistance, . . 

•0613 

•0638 

1—1 

Field, with box, .... 

5 2 ' 59 . 

53 -o 8 

s 

! 

Field, alone,. 

. . • 


p“ 

Power applied, .... 

18-89 

18-05 

5- 

3 

Total elect, energy, . . 

18-23 

17-24 

0 

p 

Ext. elect energy, . . . 

16-95 

1600 

3 

Energy in arm., .... 

•878 

•863 

p 

3 

Energy in field, .... 

•401 

•374 

n 

CfQ 

Total efficiency, .... 

96-53 

95-49 

p 

< 

Commercial efficiency, . 

89-76 

88-63 


Economic coefficient, . . 

92-99 

92-82 

p 

y c power in arm., . . . 

4-65 

4-78 


% power in field, . . . 

2-12 

2-08 


No revolutions, .... 

14008 

1389-7 


Friction of arm., .... 

. . . 

. . . 


Temp, of air,. 

26-4° C. 

2 7 ’° C. 


Temp, of pole-piece, . . 

44° C. 

45-4° C. 



This was the first machine tested and the measurements were 
intended as much to show any weak points in the method as to 
serve as a test of the dynamo. If no trouble occurred, the work 
was to be accepted, otherwise it would have been repeated after 
the causes of error had been removed. 

On looking at the table, it will be seen that the efficiencies for 
the two tests differ by about one per cent. The agreement of the 
measurements of the current and potentials as shown in the values 
of the resistances, calculated from them, is very good. Whether 
the difference is due to the power measurements, or to different 
conditions of lubrication, velocity, etc., is impossible to say. 

After the second test, the insulation of the armature gave way; 
making it impossible to repeat the full load measurements, or to 
test on the partial loads. 






















46 


EDISON NO. 10 DYNAMO. 

Diameter of armature, 9 -rk" inside; IO-I" outside. 


Weight of machine, 47 10 pounds. 

Number of commutator bars, 64 

Turns of wire in a coil, 1 

Length of useful wire in a coil, 33" 

Must brushes be adjusted ? yes. 

Diameter of bearing, 2^" 

Length of bearing, 

Number turns per minute, 1200 

Volts for best work, 125 

Amperes for best work, 200 


Table II gives the results of the measurements: 

There is little to say of the full load measurements of this 
machine. The extreme difference is about one-half per cent.; 
the greatest difference from the mean one-fourth per cent. 

The dynamo was measured twice on the partial loads. The 
first set was on the same day as the full load tests, the machine 
being run on open circuit for a couple of hours after the last full 
load measurement, then tested for quarter load, then run on half 
load for a while and tested, etc. The second set, made some days 
later, showed that the machine had not been sufficiently cooled for 
the first set of measurements. The total efficiencies, calculated 
from the two sets of measurements, differ for the quarter load about 
one and one-half per cent.; for the half load, three-quarter per 
cent., and for the three-quarter load, one-seventh per cent. 

In comparing these total efficiencies, if the difference of arma¬ 
ture friction (-152 horse-power) be applied to the first set, we get 

% load - y* load - H load. 

First set, 83-10 90-51 92*83 

Second set, 83-32 90*55 92*44 

But as the measurement of friction was made after the three- 
quarter load in each case, the values for this load should agree 
better than for the others. Part of the difference of -39 per cent, 
is undoubtedly due to the fact that in the last set of measurements 
the unsteadiness of the potential galvanometer while measuring the 
armature resistance, due to changes in the contact resistance of the 
brushes, was so great that the brushes were held against the com¬ 
mutator, thus giving too small a value of r a , and therefore of Ef v 
On the whole, the agreement of the two sets is very satisfactory. 


* The suffix e refers to lamps and d to “ dead ” resistance. 


47 


H H 

o n> 2. 

3 3 S 
V V S’ 

« o 3 


§! ^ 

• T 3 T 3 
2 ° O 

2 3 3 


c& cd 


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n> " 

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P-*• 

cd 

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P 

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d i—• ■ 


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d 


w n h w w 

° 2 2 . 3 3 

3 p ? ? 

d _ 22 CTQ 

35 

o 


o 

d 

o 

3 

o 


n> 

o 


(/i (D 

K 


3 3 

dD S 


r> 

o 

o> 

35 

o 

3* 

d 




S, 3 

f-a 

p-*» >• 

cd 

d • 

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►—» • 

3 

dN 

cd 


P 

3 


W 

x 

r-f 

CD 

rT 

p 

cd 

d 

CD 

•-t 


H 

>n 



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M 

o 

n 

H 

w 

o 

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P - * 

CD 

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CD 

►-t 

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d 

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r-f- 

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1—i 

CD 

P— • 

CL. 

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3 

p 

<—p 

CD 

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4 8 

WESTON NO. 7 M. DYNAMO. 


Diameter of armature, 

Weight of machine, 3300 

Number of commutator bars, 64 

Total number of turns in coils, 128 

Turns per commutator segment, 2 

Average length of a turn, 6 feet, 8" 

Must brushes be adjusted ? slightly. 

Diameter of bearing, pulley end, 2" 

Diameter of bearing, commutator end, 1 * 4 " 

Length of bearing, pulley end, 7 / 4 " 

Length of bearing, commutator end, 

Number of turns per minute, 1050 

Volts for best work, 160 

Amperes for best work, 125 


Table III gives the results of the measurements: 

As stated under “ potential measurements,” there was a sharp 
change in the value of the constant of the potential galvanometer 
between the second and third tests. The following are the cali¬ 
brations made : 


Time. 

Value of K 50 . 

Method. 

A. M. 

at 25 degrees. 


IOOO 

1 '3*°5 

Voltameter with standard resistance. 

11 '35 

I ' 3°7 

Current galvanometer with german-silver strips. 

P. M 



12 50 

i* 3°8 

Current galvanometer with german-silver strips. 

2-50 

00 

N 

Current galvanometer with german-silver strips. 

3'°5 

1-286 

Voltameter with standard resistance. 

4'i5 

1 286 

Voltameter with standard resistance. 


For the first two tests, the value 1*306 was used; for the last 
two, 1-286. 


The tables show a gradual decrease in the efficiencies, the dif¬ 
ference between the first and last values being about one per cent 
The cause seems to be the different amounts of lead given the 
brushes. If we compare the first with the third test, it will be 
seen that, with about the same current in the field and a greater 








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50 


number of revolutions of the armature, the E. M. F. of the latter test 
is about five volts less than that of the former. In the last test, 
with the speed still further increased and with the field current 
about constant, the E. M. F. is slightly less than in the third 
measurement. 

The partial load tests were made after the constant had become 
steady. After the three-quarter load test, a measurement was 
made on full load. As it was not made under. the provisions of 
the code, it is marked “ unofficial ” in the table. The half load 
test was repeated to check the former measurement. The differ¬ 
ence of *3 per cent in the total efficiencies is probably accounted 
for by the slight increase of armature friction caused by running 
on the three-quarter load. The greatest value of the commercial 
efficiency is on three-quarter load, the slightly less value of the 
total efficiency, as compared with the full load, being more than 
counter-balanced by the smaller loss in the armature and field. 


WESTON NO. 6 M. DYNAMO. 
Diameter of armature, 

Weight of machine, 

Number of commutator bars, 

Total number of turns, 

Turns per commutator segment, 

Average length of a turn, 

Must brushes be adjusted? 

Diameter of bearing, pulley end, 

Diameter of bearing, commutator end, 
Length of bearing, pulley end, 

Length of bearing, commutator end, 

Number of turns per minute, 

Volts for best work, 

Amperes for best work, 

Table IV gives the results of the measurements: 


9 1 // 
C -3T 

2000 

72 

144 

2 

6 feet 5" 
slightly. 

154 " 
i#" 
6 %" 
5 " 

1150 

120 

80 


The full load measurements probably agree as closely as the 
conditions of the tests. There was a good deal of sparking at the 
brushes, and the machine seemed overloaded. 

For the partial loads, the total efficiency increased up to the three- 
quarter load, and there was little sparking at the commutator. On 
the unofficial full load test, the sparking was quite violent, and the 
efficiency fell about two per cent, from the three-quarter load. Com- 


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52 


paring the unofficial full load with the tests of the day before, and 
applying the difference of armature friction to the former, it will 
be seen that the total efficiency for the unofficial test is less, the 
load being greater and the efficiency at this load decreasing rapidly 
as the load increases. 

edison no. 4 Dynamo. 

Diameter of armature, inside, 7 T 1 6 - // outside 


Weight of machine, 1470 

Number of commutator bars, 50 

Turns in one coil, 2 

Length of useful wire in a coil, 48" 

Must brushes be adjusted ? yes. 

Diameter of bearing, 

Length of bearing, 

Turns per minute, 1600 

Volts lor best work, 125 

Amperes for best work, 80 


Table V gives the results of the measurements : 

This machine was not coupled directly to the dynamometer, 
the high speed required being deemed unsafe. It was run by a 
belt from a pulley on the transmission shaft of the dynamometer. 
In allowing for the loss due to the belt, it was assumed that for the 
full load the friction of the armature was the same as that of the 
No. 5 dynamo. 

The full load tests agree very closely, the total efficiencies 
increasing slightly with the horse-power. The commercial effi¬ 
ciencies differing very little. 

The measurements on the partial loads are perhaps a little low, 
as it is probable that sufficient allowance was not made for the 
belt. The temperature was much lower than for the full load tests 
and the belt was probably stiffer. 


53 



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54 


EDISON NO. 20 DYNAMO. 


Diameter of armature, 9-Jjl 
Weight of machine, 

Number of commutator bars, 
Turns of wire in a coil, 

Length of useful wire in a coil, 
Must brushes be adjusted ? 
Diameter of bearing. 

Length of bearing, 

Number of turns per minute, 
Volts for best work, 

Amperes for best work, 


inside, JO$4 outside. 
8331 pounds. 
44 

• 59 " 
yes. 

2^" 

10 

1000 

125 

400 


Table VI gives the results of the measurements : 

The full load tests are marked unofficial, because the prelim¬ 
inary run of ten hours was not on full load. The machine was 
started at the usual time, midnight, with about the right load, but 
in a few hours the power fell to about fifty horse-power, and 
remained about the same until noon of June 19th, when by increas¬ 
ing the number of revolutions, the proper load was nearly attained. 
The tests were to have been repeated the next day, but unfortu¬ 
nately the insulation of the armature gave way, making this 
impossible. 

The tests seem to agree quite well. It is hard to compare the 
first full load measurement with the others as the conditions were 
different. The two full load measurements made under about the 
same conditions agree almost exactly. 


55 


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56 


WESTON NO. 6 W. I. DYNAMO. 
Diameter of armature, 

Weight of machine, 

Number of commutator bars, 

Total number of turns in armature coils, 
Turns per commutator segment, 

Average length, 

Must brushes be adjusted? 

Diameter of bearing, pulley end, 

Diameter of bearing, commutator end, 
Length of bearing, pulley end, 

Length of bearing, commutator end, 

Turns per minute, 

Volts for best work, 

Amperes for best work, 


2IOO pounds 

56 

I 12 

2 

6 feet, 3 
slightly 

1 Vs" 

5 " 

1200 

130 

100 


Table VII gives the results of the measurements: 

The values of the total efficiency for the different measure¬ 
ments of this machine differ widely. The first test gives a much 
smaller value than the rest, and is rejected, because, whether the 
difference is caused by errors in the measurements, or in the 
adjustment of the machine, the test evidently does not represent 
the normal efficiency of the dynamo. 



Rejected. 


57 


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On 


Table VII. — [Weston No. 6 W. I. Dynamo , ijo Volts'). 

June 22(3. June 23d. 


























































58 

Table VIII gives a summary of 




the tests 


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* Armature insulation gave way, J Average of full load measurements, 

f Unofficial. 













































59 


In the table, the full load efficiencies of the Edison No. 20 
dynamo are marked “ unofficial,” because the preliminary run was 
not in conformity with the code, not because there is any reason to 
mistrust the results. 

Of the fifty-four measurements made, four were for obvious 
reasons deemed unworthy of calculation. These were two tests of 
the Edison No. 5 dynamo, and a couple of partial load tests of the 
Weston No. 7 M machine, made while the constant of the poten¬ 
tial galvanometer was unsteady. Of the remaining fifty tests, but 
one is rejected—a full load measurement of the Weston 6 W. I. 
dynamo. 

Considering the care taken in standardizing all of the instru¬ 
ments used in the measurements, and the very close agreement of 
tests made on the same dynamo, it seems probable that the results 
given in the above table represent very nearly the efficiencies of 
the machines under the conditions of the tests. 

The dynamos were favored by being coupled directly to the 
dynamometer, and it will be seen on looking at the tables that 
the loss by friction was slight. 

In the measurements, the ohm was taken at 106 centimetres of 
mercury, so in order to reduce the values to absolute measure the 
potentials, and, therefore, the efficiencies, should be reduced by 
about one-fourth per cent. 

LOUIS DUNCAN, Chairman. 
GEO. L. ANDERSON, Secretary. 
WM. D. MARKS, 

J. B. MURDOCK, 

A. B. WYCKOFF. 













































. 












. 









































. ' ' ? . 


« 




• 
















. 
















































. 




■ 






























































■ 















































FRffiNKLIN INSTITUTE]OFTHE STATEOF PENNSYLVANIA 

■t I 

FOR THE 

Promotion of the Mechanic Arts. 


Mechanical and Electrical Tests 


OF 



Report cif a Special Committee, appointed dy 
the Fresfdenpof the Franklin Institnte in 
conformity with a Resolution of the 
Hoard of Managers, passed 
November 12, 1BB4, 


[ISSUED by AUTHORITY of the BOARD of MANAGERS and PUBLISHED as a 
SUPPLEMENT to the JOURNAL of the FRANKLIN 
INSTITUTE, NOVEMBER, 1885 .] 


PHILADELPHIA : 

THE FRANKLIN INSTITUTE. 
1885. 



















EDITING COMMITTEE. 


PERSIFOR FRAZER, Chairman , 

CHARLES BULLOCK, 

THEO. D. RAND, 

COLEMAN SELLERS, 

WILLIAM H. WAHL 



FRANKLIN INSTITUTE OF THE STATE OF PENNSYLVANIA. 
FOR THE PROMOTION OF THE MECHANIC ARTS. 


Mechanical and Electrical Tests of Conducting Wires 


To the Board of Managers of the Franklin Institute: 

Gentlemen :—I herewith transmit the report of the Committee, 
consisting of Lieut. George L. Anderson, U. S. A., for the electrical 
tests, and Mr. J. W. Grant, Engineer of Tests (Fairbanks & Co.), for 
the mechanical tests, appointed under authority of the resolution of 
the Board, adopted November 12, 1884, to conduct examinations 
and tests of conducting wires exhibited at the Electrical Exhi¬ 
bition. Very respectfully, 

W. P. Tatham, President. 

Philadelphia, September 3, 1885. 


Mr. William P. Tatham, 

President of the Franklin Institute, Philadelphia: 

Sir :—I have the honor to transmit herewith the results of 
electrical tests made on various kinds of wires, sent for trial to the 
Philadelphia Electrical Exhibition of 1884. The data contained 
in the left half of the sheet were copied from the labels found 
attached to the coils of wire, and in two or three instances it will 
be seen that the number of the gauge does not agree with the 
diameter measured. It is thought, therefore, that some of the 
labels may have been misplaced before the coils reached the 
Franklin Institute. The figures in the right half of the sheet 
were those obtained from measurement. The length given in 
column VI is that portion of the coil of which the resistance was 
measured, and which is given in column VIII. 

I am, very respectfully, your obedient servant, 

George L. Anderson, U. S. A. 


Newport, R. I., July 19, 1885. 





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